There have been conventionally developed and operated systems that include sensor nodes placed in a wide area and make a processing device capable of communicating with the sensor nodes via radio waves obtain and analyze values measured by the sensor nodes. For example, the processing device that has received measured values of sewer water levels or gas concentrations transmitted from the sensors located on the back sides of manhole covers performs diagnosis with the measured values to detect the state inside the manhole.
When radio communication is used for communication between the sensor node and the processing device, communication failure such as shielding by vehicles or interference from peripheries may occur, preventing the processing device from obtaining measured values. Thus, technologies for detecting anomalies of radio communication with a high degree of accuracy are important.
A method that detects anomalies by comparison with a cluster generated from observation data at normal time has been known as the technology for detecting anomalies of radio communication as disclosed in, for example, Japanese Patent Application Publication No. 2016-33778 (Patent Document 1). The art of Patent Document 1 is an anomaly diagnosis and preventive maintenance system for mechanical equipment, generates a cluster of each period of time with normal time-series data based on an operation schedule, and performs the comparison with the cluster to detect an anomaly.